This was my logic too so I applied it and it worked well for me. When I noticed that PH had already wedged a black plastic space between the frame and the camera tray, which was clearly there to create resistance, I just thought that this would be a better idea and would not wear with time. As I mentioned several pages ago: remove that black plastic spacer, fire up you AV300 and RSGS and watch the whole thing as it the jitter builds upon itself and goes completely out of control. If you put the spacer back in it stops (to some degree if you have tightened your mounting screw just right). With the rotary damper you don't have to worry about adjusting the screw just right right. If the damper has just the right amount of resistance you can simply count on it to do its job each time. This simple fix worked very well for me. It works with my GoPro, my 5D Mark 2 and my T2i.
One day I was out in the noon sun on a 109 degree day in LA on my hands and knees trying to dig a hole under the sidewalk in front of my house so that I could pass a piece of PVC pipe through there to setup sprinklers in this area that otherwise has no water available. I thought I was going to drop dead of a heart attack... and that was 30 years ago. A 5 year old Mexican boy with a white hat and chrome 6-shooters stopped to watch me... and finally said; "Why you don't just do what WE do?" I said, "Okay smart guy what do YOU do?" He showed me that they take a piece of PVC, duct tape it to the garden hose, turn on the water and let the water do the digging as it bores its own hole through the dirt, under the sidewalk and then comes out the other end. 5 years old. It worked. From that point on I learned that anyone can have an idea that might be worth listening too. Even a moron.
LOL - and I thought 5-year-olds could only embarrass us oldies with their computer skills
I think that your damper solution is absolutely valid - to fix the gimbal, not the gimbal controller. As Denny says - if hard-mounting the RSGS is passing vibration into the sensors then it makes sense to prevent that first, then see what can be improved on the gimbal itself. Denny's solution needs some work to establish the right level of isolation to overcome the problem without introducing new ones - one of the keys there is a lead washer to create inertia and mass: that solution may not appeal to all.
In an ideal gimbal, the mechanical arrangement of each axis must be "stiff" (in the engineering sense), i.e. rigid and without any radial or axial play whilst still having very low friction. Any friction present must be overcome by the servo before any actual movement can take place. This means 1) a delay and 2) a jolt in the system as the friction is overcome and the rotation accelerates more than was originally intended. Any play in the system (a.k.a. looseness, slop, backlash, etc.) must also be "taken up" before any actual movement of the axis can take place. Unfortunately the PH gimbals are poorly designed in this respect - as far as I know, neither side of the pitch axis (for example) has any pre-loading on the bearings or special bearing arrangement to limit/remove radial and axial play. The servos have (unavoidable) backlash in their gears and the belt drive has (unavoidable) backlash. The net effect of all of this is that the camera is
not rigidly fixed in its orientation - it can "wander about" either side of its nominal position by an amount equal to the sum of all the backlash in all the components. And it's easy to see - with the servo holding any particular position, try moving the camera
very gently - it will be able to move (in just about every direction, but rotation will be the most obvious). This unconstrained movement
will show up in video, particularly at longer focal lengths. It's one of the big advantages of the Zenmuse, which (by its mechanical design and the absence of any gearing between the motor and the camera) will have (almost) zero backlash: it is a "stiff" structure end-to-end.
The primary reason for the appearance of belt drive on this type of gimbal is because it will tend to mask the backlash in the servo (which is far and away the worst offender). The belt tension creates a radial bias force on the axis - in other words, a frictional force that needs to be overcome before that axis can rotate. This will
mask, to some extent, the backlash in the servo but it won't
reduce it in any way. Note, too, that its effectiveness at masking the backlash will vary according to how tight it is fitted. Furthermore, of course, it also introduces its own backlash to the system. As with any gearing, the belt drive also has the simultaneous effect of reducing the drive speed and increasing the torque by the same proportion. Increased torque is helpful but reduced speed isn't!
This backlash has another nasty trick up its sleeve - if your axis measurement system (in this case the RSGS) is able to "see" that unconstrained movement, i.e. it senses the axis/camera has rotated when actually it hasn't (it's just "flopped" from one side of the backlash to the other) then it thinks "ooh! I must correct that!" and tries to do so. Through the miracle of mathematics, this can quickly become a meaningless oscillation as the system bounces from one end of the backlash to the other (and beyond, thanks to momentum) and the controller battles to "correct it". High speed oscillation... a.k.a. jitter. The only way to stop the maths misbehaving like this would be to filter out tiny movements, in other words, reduce the resolution of the system. The maths can't tell the difference between backlash and rotation of the frame in the air.
Fitting a rotary damper is supplementing the "masking" of backlash on that axis - as such it will be effective in preventing backlash-induced jitter (and should allow you to have the gain higher so you have a more responsive axis). You want a low resistance, just enough to stop the axis "flopping" and not enough to hold the servo back too much when it does try to rotate the axis. As you say: more controllable and constant than a friction washer (or adjusting the tension of the belt). There are adjustable bi-directional rotary dampers available, of course - that would be ideal to fine tune the effect. But, at the end of the day, the backlash will still be there - a better mechanical design of the gimbal as a whole would remove the need (for the RSGS or any other controller).
